1. Field of the Invention
This invention relates to a defect-recognition processing apparatus for recognizing linear crystal defects, such as stacking faults, on the surface of a semiconductor wafer.
2. Description of the Related Art
When manufacturing a semiconductor device using a silicon wafer, it is necessary to suppress the development of crystal defects, such as a dislocation or stacking fault, which cause downgrading of the electric characteristics of devices. Crystal defects occur when the arrangement of the silicon atoms in the wafer is disturbed, and are a cluster of point defects developed from the nuclei of microdefects in the wafer or from the nuclei resulting from a contamination by heavy metals at the steps of a thermal treatment, such as thermal oxidation or diffusion.
One of the quality evaluation standards for wafers is the checking or evaluation of the density of stacking faults developed on the surface of a wafer after the wafer has been oxidized. This evaluation is performed by eliminating an oxide film formed on the wafer surface, etching the wafer surface by means of a highly selective etching solution, observing the surface state under an optical microscope or a scan type electron microscope, detecting faults or defects under the configuration classification of dirt or surface scratches and counting the number of defects detected. The sizes of defects, though depending upon the heat-treatment step, are usually of the order of 0.5 to 20 .mu.m. The size of the defects needs to be enlarged to a magnitude of about 50 .times. to 1000 .times. for observation. In order to detect the defects with high accuracy in view of the lowered control standard against the defect density (for example, 0 to 10 pieces/cm.sup.2), it is necessary to enlarge the observation area to be evaluated from the stochastic viewpoint. Thus the "gross" observation of crystal defects in reality is restricted. When the control standard value of the defect density is 100 pieces/cm.sup.2, 1 piece/cm.sup.2 and 0.1 piece/cm.sup.2, it is possible to accurately control the defect density by observing the microscopic field view of over 1/100 cm.sup.2, over 1 cm.sup.2 and over 10 cm.sup.2, respectively. It takes about one second per field to recognize defects. Thus it takes about 2 to 5 hours per piece of a silicon wafer 125 mm in diameter. Where a great number of silicon wafers are to be processed, a great variation (.times. 2 to 4) in the results of observation occurs due to the physical limitations, such as the eyestrain and disturbed concentration of the observer, failing to make proper observation.
A defect-recognition processing apparatus has been proposed which picks u an image corresponding to that area of the wafer which is being enlarged by the microscope, and detects a defect image on the image screen through pattern recognition. However, the apparatus suffers from disadvantages from the standpoint of utility, such as a lowered rate of recognition, a lowered processing speed, and high manufacturing cost. The term "the rate of recognition" means: ##EQU1##
The same characteristic can equally be true of not only defects on the surface of the semiconductor wafers but also defects on the surface of other objects, such as metal.